Manufacture of microelectronic devices and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, patterned metal layers forming the micro-scale devices are created.
The substrate is electroplated in a plating apparatus or chamber, with one side of the substrate in a bath of liquid electrolyte, and with electrical contacts touching a conductive layer on the substrate surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte plate out onto the substrate, forming a metal film on the substrate. To better achieve uniform plated film thickness, the plating apparatus may have an annular dielectric shield, which shields or reduces the electric field in the electrolyte near the edge of the substrate.
Achieving a uniformly thick plated metal film can be difficult, for various reasons. In Damascene plating, the sheet resistance of the film changes during the plating process, which alters the electric field within the plating apparatus and tends to cause the plated film at the wafer edge to be thicker. In wafer level packaging applications, the active plating area around the edge of the wafer can vary significantly, depending on the patterns on the wafer. The active plating area may also vary depending on the specified edge exclusion zone or dimension. Substrate diameters may also vary by up to several millimeters. This can cause variations in the plated metal film near the perimeter of the substrate, due to the varying geometries resulting from changing substrate diameters.
In present electroplating apparatus, to achieve optimum plating results, the electric field shields must be changed to match the characteristics of the wafer. As changing the shields is time consuming, there is a need for plating apparatus that can adjust for a changing wafer active area without having to change the shields.